A Complete Active Space Self-Consistent Field and Density Functional Theory Study of S0, T1, S1 States of Five Phenol ortho-Derivatives

Abstract

The usual polar effects of substituents will operate from the o-position not less than from the p-position, but in the o-substituted compounds there is evidence of some additional factor which is absent in the isomeric derivatives and this additional factor is defined as ortho-effect. Meyer emphasized the fact that the ortho-effect does not depend upon the chemical nature of the substituent, but appears rather to be governed by its size (as measured, according to him, by the weights of the atoms) 1. The strengths of aromatic acids and bases are also profoundly influenced by substituents in the o-position and analogies are found in phenomena such as the greater strength of allocinnamic acid than of cinnamic acid 2. The classical dissociation constants of Ostwald and others indicate that all o-substituted benzoic acids are stronger than benzoic acid itself and often considerably stronger than their m-and p-isomers and this is confirmed by recently measured thermodynamic constants for benzoic acid as unity. ortho-Effect has not been widely investigated and used in organic synthesis, but also found important implications in photochemistry 3-5. There are some investigations of the ortho-effect on the photodissociation dynamics 6-9. Shao and Baer found that the NO2 and NO fragment channels have been observed for three nitrotoluene isomers and significant OH production was observed in the dissociation of o-nitrotoluene and this was attributed by ortho-effect which involves a bicyclic intermediate and subsequent rearrangement to the nitrite form prior to fragmentation 8. The product internal energy distributions